Norwalk-Like Viral Gastroenteritis
in U.S. Army Trainees -- Texas, 1998

During August 27-September 1, 1998, 99 (12%) of 835 soldiers
in one
unit at a U.S. Army training center in El Paso, Texas, were
hospitalized
for acute gastroenteritis (AGE). Their symptoms included acute
onset of
vomiting, abdominal pain, diarrhea, and fever. Review of medical
center
admission records for AGE during the previous year indicated that
fewer
than five cases occurred each month. This report describes the
outbreak
investigation initiated on August 30 by a U.S. Army Epidemiologic
Consultation Service (EPICON) team; the findings indicated the
outbreak was
caused by a Norwalk-like virus (NLV).

The EPICON team reviewed data from the inpatient records of 90
ill
soldiers. AGE was defined as three or more loose stools and/or
vomiting
within a 24-hour period in a soldier or employee at the training
center
during August 26-September 1. Illness was accompanied by a
minimally
elevated leukocyte count, mild thrombocytopenia, and low-grade
fever. The
median duration of hospitalization was 24 hours (range: 12-72
hours). Stool
samples collected from persons with AGE on hospital admission were
negative
for bacterial and parasitic pathogens. Of 24 stool specimens sent
to CDC
for viral agent identification, 17 were positive by reverse
transcriptase
poly-merase chain reaction assays for NLVs (genogroup 2).

Interviews with foodhandlers in the base's two dining
facilities (DF1
and DF2) revealed illness in a confection baker, who had become ill
in DF1
while baking crumb cake, pie, and rolls on August 26. One other DF1
employee who was not a foodhandler also reported self-limited
gastrointestinal illness during August 27-29. No worker in DF2
reported
illness.

Cultures of food specimens from the ice cream dispenser in DF1
grew
nonpathogenic coliform bacteria (Citrobacter diversus and Serratia
liquefaciens); however, the sample was at room temperature before
culture.
Enterobacter cloacae coliform bacteria were cultured from the soda
fountain
in DF2. Water samples taken from multiple sites in the training
compound
and from elsewhere on post were all negative for coliform
contamination.

A questionnaire about food preferences, based on the previous
week's
menu, was administered to 86 hospitalized soldiers (84 of whom had
eaten in
DF1 during the 10 days before answering the questionnaire) and to
237
randomly selected soldiers from the training unit. Of the 237
nonhospitalized soldiers, 41 (17%) did not eat at DF1 during the 10
days
before answering the questionnaire; 40 (17%) had illnesses that met
the
case definition. Thus, cases of AGE were characterized in 126
soldiers
(Figure_1).

To determine the point source of the outbreak, cases with
onset during
August 27-28 (n=98) were analyzed separately for odds ratios (ORs)
of
selected exposures (Table_1). The univariate OR for illness
associated
with dining at DF1 during the week before the outbreak was 9.8 (95%
confidence interval=2.8-40.2). Two soldiers who ate exclusively at
DF2
became ill, and one ill soldier reported not eating at either
facility.
Food items (crumb cake, pie, cinnamon rolls, and ice cream) and
soda
fountain dispensers were associated with illness by univariate
analysis.
Using multivariate analysis, only DF1 and the carbonated beverage
dispensers remained strongly associated with illness (Table_1).

Editorial Note

Editorial Note: NLVs, previously known as small round-structured
viruses,
are the most common cause of nonbacterial gastroenteritis outbreaks
in
adults (1,2). Classified in the family Caliciviridae (1,2), NLVs
are
transmitted by the fecal-oral route and have been implicated in
42%-71% of
viral outbreaks associated with contaminated water and food since
the
Norwalk virus was identified (1,3,4). NLV outbreaks have been
caused by
eating contaminated raw shellfish and by unsanitary food
preparation
practices by foodhandlers (1,3-6). NLVs are hardy, ubiquitous, and
extremely persistent in the environment, resisting disinfection and
chlorination, and have caused serial gastroenteritis outbreaks
(1,3,4).

The epidemiologic evidence described in this report indicates
that the
outbreak was a point-source, propagated, foodborne viral illness.
Although
cases occurred before the onset of acute illness in the confection
baker,
he could have been the point source because he probably shed virus
before
the onset of clinical symptoms. The strong association with
drinking
carbonated beverages is not easily explained and may represent
increased
thirst among ill persons. The use of the Army hospital as a
quarantine bay
probably decreased secondary propagation of the illness.

Prevention of future outbreaks of NLVs in U.S. military dining
facilities or any food service establishment depends on vigilance
and
rigorous enforcement of simple measures to prevent food
contamination.
These measures include handwashing, exclusion of ill foodhandlers
from the
workplace, and basic hygiene and sanitation measures.

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